1. Field of the Invention
The present invention relates to a reading apparatus such as an image sensor of contact-type adapted such that photoelectric converter element array is arranged therein which virtually corresponds to an original document in a dimension of 1:1 and relates to a producing method therefor, aiming for miniaturization of, for example a facsimile apparatus.
2. Description of the Prior Art
In such an apparatus, it is desired that the degree of clarity (contrast) and reproducibility of the reading image be both improved to effect a faithful reading of the image. Furthermore the improvement in the productivity of such reading apparatus is desired. However, the prior art has fail to sufficiently make improvements in the degree of clarity (contrast), the reproducibility, and the productivity.
Of late, development of a facsimile apparatus of contact-type has become active. For such apparatus, it has been proposed to present such various types as that detecting the light reflected from an original document through a focusing rod lense array, or that effecting the excellent light-transmittivity and the miniaturization without such array.
FIG. 1 is a perspective view showing a photo-detection part 2 in the reading apparatus of the prior art employing the focusing rod lense array. On a substrate 5, there are formed a common electrode 6 to be one electrode commonly for each photoelectric converter element, a photoconductor 7, and transparent electrodes 8 successively in this order as shown in FIG. 1. Additionally light-excluding metal layers 9 are applied on the transparent electrodes 8 except on light-introduction portions 10 for reflected light A. A transparent protective layer 11 made of SiO.sub.2 etc is so applied as to cover the common electrode 6, photoconductor 7, transparent electrodes 8, and light-excluding metal layers 9. A drive circuit part 12 such as a shift register is also provided on the substrate 5.
According to such conventional apparatus, the reflected light A from an original document 1 is passed through the transparent protective layer 11 and is received by the light-introduction portions 10, and then reading picture elements corresponding to the individual light-introduction portions 10 are produced.
However, the transparent protective layer 11 made of SiO.sub.2 is formed by means of sputtering method, or by applying alkoxide solution and heating the thus applied solution at approximately 400.degree. to 500.degree. C. in the above conventional apparatus, which leads to production of plasma or a temperature rise. Such severe layer-forming conditions reduce the quality of exposed portions of the photoconductor 7 made of amorphous silicon or the like which has already been formed. It has been found that dark current is remarkably increased to deteriorate the S/N ratio consequently.
FIG. 2 shows a partial section taken along the line II--II of FIG. 1. As understood from FIG. 2, of the photoconductor 7, both portions 7a intervening between elements and portions 7b in the vicinity of the light-excluding metal 9 are also irradiated with light. As a result, the intervening portions 7a decrease in resistance value to produce leakage current among the adjoining elements. Hence, the reading picture element decreases in clarity. In addition, the portions 7b decrease in resistant value to produce leakage current between the electrodes 6 and 8. It has been found that dark current extremely increases to deteriorate the S/N ratio consequently.
FIG. 3 shows another type of the photo-detection part 2 of the prior art. On a light-transmitting substrate 13, there are formed a light-excluding metal layer 15 having formed therein light-passing holes 14 for passing the reflected light C from the original document 1, a light-transmitting electrically insulative layer 16, light-transmitting individual electrodes 17 provided in the respective photoelectric converter elements, a photoconductor 18, and a common electrode 19 to be one electrode commonly for each photoelectric converter element, successively in this order, as shown in FIG. 3. Also in the photo-detection part 2 of this type is provided a drive circuit 20.
According to this conventional apparatus, the light C reflected from the original document 1 comes from the side of the light-transmitting substrate 13, and is passed through the light-passing holes 14 corresponding to the respective photoelectric converter elements. Then, photocurrent is produced in the photoconductor 18, thus resulting in reading picture elements.
According to a process of producing this apparatus, however, there are to be formed on the light-transmitting substrate 13, the light-excluding metal layer 15 normally made of Al, Cr, or the like by means of vacuum vapor deposition, the light-transmitting electrically insulative layer 16 made of SiO.sub.2 or the like by means of sputtering method, the light-transmitting individual electrodes 17 made of ITO (tin-indium oxide) or the like by means of vacuum vapor deposition method, the amorphous silicon photoconductor 18 by means of glow discharging method, and the common electrode 19 made of Al, Cr, and the like by means of vacuum vapor deposition method, successively in this order. Accordingly, it is impossible to form two layer of these five layers 15, 16, 17, 18 and 19 successively by means of the same thin film forming technique. Therefore, in order to form these layers it is required to use the suitable thin film forming apparatus depending on the layer to be formed. On the contrary, it is desirable to form at least two layers by a series of process of the same thin film forming technique in the light of the shrinkage of the required time or the improvement on the efficiency of the process.
Besides, there is a possibility that a short takes place between the light-excluding metal layer 15 and the light-transmitting individual electrodes 17 when pin-holes are produced in the light-transmitting electrically insulative layer 16. In consequence, such a problem is caused that the individual electrode 17 is electrically connected with other electrodes 17 via the light-excluding metal layer 15, thereby preventing the accurate reading picture elements from appearing and thus lacking in the reliability.